The global aim of the proposed project is to identify and understand the genetic determinants of alcohol dependence, comorbid nicotine dependence, and other drug dependence in African-Americans. To date, the majority of genetic findings related to addiction have come from samples of primarily European descent. With the large volume of data emerging from genome-wide association studies (GWASs) of alcohol dependence and related disorders, replication and validation across populations will play critical roles in solidifying knowledge about genetic determinants of these disorders. Because these emerging GWASs are largely being conducted primarily in samples of European descent, findings from them will need to be validated across populations. Cross-population validation is a key aspect of the gene-discovery process because allele frequencies differ across ethnic groups. In addition, differences in linkage-disequilibrium patterns between African-American and European-American samples can be used to refine genetic signals initially identified in populations of European descent. Hence, this sample would facilitate the important steps of validation and refinement of genetic findings. The project will ascertain 1,000 cases and 1,000 controls matched on gender, age, zip code, and education, from the African-American community. Cases will consist of subjects seeking treatment for alcohol dependence, either alone, or comorbid with other drug dependence; controls will comprise subjects who have consumed alcohol, but are not dependent on alcohol or other substances. Men and women will be equally represented among both cases and controls, so that maximal power to detect gender specific associations is obtained. Thorough assessment of alcohol dependence, comorbid drug dependence, psychiatric disorders, and risk factors will be carried out with widely-used, diagnostic interviews with high reliability and established validity. Genes from published association studies in samples of European or European-American descent, and findings from emerging GWASs in predominantly White samples will be tested for association with alcohol dependence in this African-American sample. Positive findings will be further refined by testing for association with other substance dependence, comorbid psychiatric disorders, and phenotypes related to general addiction liability and externalizing behavior. These analyses will allow determination of whether previous association findings for substance dependence are generalizable to the African-American population, and whether association with other population-specific variants is observed in the candidate gene regions. State-of-the art methods will be used to ensure thorough coverage of candidate gene regions, and genomic control SNPs will be used to test for potential population stratification. In summary, this project would be among the first genetic studies of alcohol dependence to focus specifically on African- Americans, thus addressing a significant public health problem in an under-studied and underserved population.